During the course of post-operative surgery, inhalation therapy is employed to maintain proper functioning of the lungs and to maintain the lungs free of fluid. Incentive spirometers are provided in the prior art which encourage the post-surgical patient to breathe at a desirable flow rate or until a desirable volume has been inhaled. These prior art incentive spirometers are typically constructed such that when a patient inhales through a tube placed in his or her mouth, a visual reward is provided for the patient. In the most common form of incentive spirometers, this visual reward takes the form of a lightweight sphere disposed in a transparent cylindrical column of slightly larger diameter than the diameter of the sphere. The column and sphere are disposed in the inhalation flow path and the flow rate of air inhaled by the patient causes the sphere to rise in the cylindrical column. Incentive spirometers of this type are inexpensively constructed of plastic materials so that they are suitable for disposability after use by each patient. In addition, these devices are easily held and utilized by nearly every patient. Further, only a short training period is required to teach the patient how to correctly use this type of device. The patient is readily interested in achieving the incentive of raising the ball in the column to a prescribed height and holding it there as long as possible by an extended inhalation. One disadvantage of prior art incentive spirometers of the type described is that they include no accurate self-contained means for measuring air displacement. Such an indication is considered quite important in continued therapy for the post-operative patient. Maintaining the sphere at the prescribed height in the cylinder does, in fact, correspond to an inhalation rate which has been prescribed by the therapist for that particular patient. The patient achieves a specific volume of inhalation by holding the inhalation rate for a period of time specified by the therapist; or, more typically, holding the inhalation for as long as the patient is able to sustain such rate. However, in order to interpret this relationship and produce an air displacement volume indication, a means of recording the length of time that the sphere has been held in place must be included. The use of timing devices which are not self-contained in the spirometer tend to complicate the procedure with the result that the patient tends to lose interest.
Another problem with prior art incentive spirometers of the flow rate type resides in the fact that the patient quickly learns how to achieve the incentive by cheating with short, quick inhalation bursts. In other words, the sphere can be raised in the cylinder by sudden bursts of inhalation. The patient, in his or her mind, has achieved the object of the incentive spirometer by moving the sphere some distance with an inhalation; however, the patient has not achieved the results necessary for therapy, namely achieving a long slow inspiratory effort at some prescribed flow rate. The inhalation bursts negate the intended goal of incentive spirometry in three (3) ways: (a) the patient does not achieve a sustained flow rate; (b) the patient does not achieve full use of his or her lungs to provide for normal exchange of gases; and (c) in the extreme case, the patient can hyperventilate while achieving the visual reward of raising the ball with a short burst.
The effort required to raise the sphere in the cylinder in spirometers of the type described is a function of many variables, such as air passage diameters, bends and other restrictions in the passages, mouthpiece design, the size of air inlets, the diameter and mass of the sphere, and the distance which the sphere must rise. There are a variety of prior art devices available, which represent a wide variation in the manner in which incentive is achieved. For example, in one device, a valve is employed to vary the effort required to raise the sphere. In another device, plural spheres are employed, each requiring a faster rate of inhalation to be lifted in a cylinder, and the incentive is for the patient to raise the spheres in sequence. These devices have largely not been successful in requiring the patient to inhale at a gradually increasing flow rate.
It is therefore an object of the present invention to provide an incentive spirometer having a self-contained means of recording the length of time during which an inspiratory incentive is achieved. It is a further object of the present invention to provide such an incentive spirometer which, nonetheless, is sufficiently inexpensive to be disposable.
It is a further object of the present invention to provide an indication each time a patient inhales at least a predetermined minimum volume of air.
It is also an object of the present invention to provide an incentive spirometer having a built-in feature which precludes a patient from achieving the incentive by means of short inhalation bursts.